Internet Engineering Task Force (IETF) S. Previdi, Ed.
Request for Comments: 7810 Cisco Systems, Inc.
Category: Standards Track S. Giacalone
ISSN: 2070-1721 Microsoft
D. Ward
Cisco Systems, Inc.
J. Drake
Juniper Networks
Q. Wu
Huawei
May 2016
IS-IS Traffic Engineering (TE) Metric Extensions
Abstract
In certain networks, such as, but not limited to, financial
information networks (e.g., stock market data providers), network-
performance criteria (e.g., latency) are becoming as critical to
data-path selection as other metrics.
This document describes extensions to IS-IS Traffic Engineering
Extensions (RFC 5305) such that network-performance information can
be distributed and collected in a scalable fashion. The information
distributed using IS-IS TE Metric Extensions can then be used to make
path-selection decisions based on network performance.
Note that this document only covers the mechanisms with which
network-performance information is distributed. The mechanisms for
measuring network performance or acting on that information, once
distributed, are outside the scope of this document.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7810.
Previdi, et al. Standards Track [Page 1]

RFC 7810 IS-IS TE Metric Extensions May 20161. Introduction
In certain networks, such as, but not limited to, financial
information networks (e.g., stock market data providers), network-
performance information (e.g., latency) is becoming as critical to
data-path selection as other metrics.
In these networks, extremely large amounts of money rest on the
ability to access market data in "real time" and to predictably make
trades faster than the competition. Because of this, using metrics
such as hop count or cost as routing metrics is becoming only
tangentially important. Rather, it would be beneficial to be able to
make path-selection decisions based on performance data (such as
latency) in a cost-effective and scalable way.
This document describes extensions (hereafter called "IS-IS TE Metric
Extensions") to the IS-IS Extended Reachability TLV defined in
[RFC5305], that can be used to distribute network-performance
information (such as link delay, delay variation, packet loss,
residual bandwidth, and available bandwidth).
The data distributed by the IS-IS TE Metric Extensions proposed in
this document is meant to be used as part of the operation of the
routing protocol (e.g., by replacing cost with latency or considering
bandwidth as well as cost), to enhance Constrained-SPF (CSPF), or for
other uses such as supplementing the data used by an ALTO server
[RFC7285]. With respect to CSPF, the data distributed by IS-IS TE
Metric Extensions can be used to set up, fail over, and fail back
data paths using protocols such as RSVP-TE [RFC3209].
Note that the mechanisms described in this document only disseminate
performance information. The methods for initially gathering that
performance information, such as described in [RFC6375], or acting on
it once it is distributed are outside the scope of this document.
Example mechanisms to measure latency, delay variation, and loss in
an MPLS network are given in [RFC6374]. While this document does not
specify how the performance information should be obtained, the
measurement of delay SHOULD NOT vary significantly based upon the
offered traffic load. Thus, queuing delays SHOULD NOT be included in
the delay measurement. For links such as Forwarding Adjacencies,
care must be taken that measurement of the associated delay avoids
significant queuing delay; that could be accomplished in a variety of
ways, including either by measuring with a traffic class that
experiences minimal queuing or by summing the measured link delays of
the components of the link's path.
Previdi, et al. Standards Track [Page 3]

RFC 7810 IS-IS TE Metric Extensions May 20161.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lowercase uses of these words are not to be
interpreted as carrying the significance described in RFC 2119.
2. TE Metric Extensions to IS-IS
This document registers new IS-IS TE sub-TLVs that can be announced
in the "Sub-TLVs for TLVs 22, 23, 141, 222, and 223" registry in
order to distribute network-performance information. The extensions
in this document build on the ones provided in IS-IS TE [RFC5305] and
GMPLS [RFC4203].
IS-IS Extended Reachability TLV 22 (defined in [RFC5305]), Inter-AS
Reachability Information TLV 141 (defined in [RFC5316]), and MT-ISIS
TLV 222 (defined in [RFC5120]) have nested sub-TLVs that permit the
TLVs to be readily extended. This document registers several sub-
TLVs:
Type Description
----------------------------------------------------
33 Unidirectional Link Delay
34 Min/Max Unidirectional Link Delay
35 Unidirectional Delay Variation
36 Unidirectional Link Loss
37 Unidirectional Residual Bandwidth
38 Unidirectional Available Bandwidth
39 Unidirectional Utilized Bandwidth
As can be seen in the list above, the sub-TLVs described in this
document carry different types of network-performance information.
The new sub-TLVs include a bit called the Anomalous (or "A") bit.
When the A bit is clear (or when the sub-TLV does not include an A
bit), the sub-TLV describes steady-state link performance. This
information could conceivably be used to construct a steady-state
performance topology for initial tunnel-path computation, or to
verify alternative failover paths.
Previdi, et al. Standards Track [Page 4]

RFC 7810 IS-IS TE Metric Extensions May 2016
When network performance violates configurable link-local thresholds,
a sub-TLV with the A bit set is advertised. These sub-TLVs could be
used by the receiving node to determine whether to fail traffic to a
backup path or whether to calculate an entirely new path. From an
MPLS perspective, the intent of the A bit is to permit label switched
path ingress nodes to determine whether the link referenced in the
sub-TLV affects any of the label switched paths for which it is
ingress. If they are affected, then they can determine whether those
label switched paths still meet end-to-end performance objectives.
If not, then the node could conceivably move affected traffic to a
pre-established protection label switched path or establish a new
label switched path and place the traffic in it.
If link performance then improves beyond a configurable minimum value
(reuse threshold), that sub-TLV can be re-advertised with the A bit
cleared. In this case, a receiving node can conceivably do whatever
re-optimization (or failback) it wishes to do (including nothing).
Note that when a sub-TLV does not include the A bit, that sub-TLV
cannot be used for failover purposes. The A bit was intentionally
omitted from some sub-TLVs to help mitigate oscillations. See
Section 5 for more information.
Consistent with existing IS-IS TE specification [RFC5305], the
bandwidth advertisements defined in this document MUST be encoded as
IEEE floating-point values. The delay and delay-variation
advertisements defined in this document MUST be encoded as integer
values. Delay values MUST be quantified in units of microseconds,
packet loss MUST be quantified as a percentage of packets sent, and
bandwidth MUST be sent as bytes per second. All values (except
residual bandwidth) MUST be calculated as rolling averages where the
averaging period MUST be a configurable period of time. See
Section 5 for more information.
3. Interface and Neighbor Addresses
The use of IS-IS TE Metric Extensions sub-TLVs is not confined to the
TE context. In other words, IS-IS TE Metric Extensions sub-TLVs
defined in this document can also be used for computing paths in the
absence of a TE subsystem.
However, as for the TE case, Interface Address and Neighbor Address
sub-TLVs (IPv4 or IPv6) MUST be present. The encoding is defined in
[RFC5305] for IPv4 and in [RFC6119] for IPv6.
Previdi, et al. Standards Track [Page 5]

RFC 7810 IS-IS TE Metric Extensions May 20164. Sub-TLV Details4.1. Unidirectional Link Delay Sub-TLV
This sub-TLV advertises the average link delay between two directly
connected IS-IS neighbors. The delay advertised by this sub-TLV MUST
be the delay from the local neighbor to the remote one (i.e., the
forward-path latency). The format of this sub-TLV is shown in the
following diagram:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A| RESERVED | Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
where:
Type: 33
Length: 4
A bit: The A bit represents the Anomalous (A) bit. The A bit is set
when the measured value of this parameter exceeds its configured
maximum threshold. The A bit is cleared when the measured value
falls below its configured reuse threshold. If the A bit is clear,
the sub-TLV represents steady-state link performance.
RESERVED: This field is reserved for future use. It MUST be set to 0
when sent and MUST be ignored when received.
Delay: This 24-bit field carries the average link delay over a
configurable interval in microseconds, encoded as an integer value.
When set to the maximum value 16,777,215 (16.777215 sec), then the
delay is at least that value and may be larger.
Previdi, et al. Standards Track [Page 6]

RFC 7810 IS-IS TE Metric Extensions May 20164.2. Min/Max Unidirectional Link Delay Sub-TLV
This sub-TLV advertises the minimum and maximum delay values between
two directly connected IS-IS neighbors. The delay advertised by this
sub-TLV MUST be the delay from the local neighbor to the remote one
(i.e., the forward-path latency). The format of this sub-TLV is
shown in the following diagram:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A| RESERVED | Min Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED | Max Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
where:
Type: 34
Length: 8
A bit: This field represents the Anomalous (A) bit. The A bit is set
when one or more measured values exceed a configured maximum
threshold. The A bit is cleared when the measured value falls below
its configured reuse threshold. If the A bit is clear, the sub-TLV
represents steady-state link performance.
RESERVED: This field is reserved for future use. It MUST be set to 0
when sent and MUST be ignored when received.
Min Delay: This 24-bit field carries the minimum measured link delay
value (in microseconds) over a configurable interval, encoded as an
integer value.
Max Delay: This 24-bit field carries the maximum measured link delay
value (in microseconds) over a configurable interval, encoded as an
integer value.
Implementations MAY also permit the configuration of an offset value
(in microseconds) to be added to the measured delay value, to
facilitate the communication of operator-specific delay constraints.
It is possible for the Min and Max delay to be the same value.
Previdi, et al. Standards Track [Page 7]

RFC 7810 IS-IS TE Metric Extensions May 2016
When the delay value (Min or Max) is set to the maximum value
16,777,215 (16.777215 sec), then the delay is at least that value and
may be larger.
4.3. Unidirectional Delay Variation Sub-TLV
This sub-TLV advertises the average link delay variation between two
directly connected IS-IS neighbors. The delay variation advertised
by this sub-TLV MUST be the delay from the local neighbor to the
remote one (i.e., the forward-path latency). The format of this sub-
TLV is shown in the following diagram:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED | Delay Variation |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3
where
Type: 35
Length: 4
RESERVED: This field is reserved for future use. It MUST be set to 0
when sent and MUST be ignored when received.
Delay Variation: This 24-bit field carries the average link delay
variation over a configurable interval in microseconds, encoded as an
integer value. When set to 0, it has not been measured. When set to
the maximum value 16,777,215 (16.777215 sec), then the delay is at
least that value and may be larger.
Previdi, et al. Standards Track [Page 8]

RFC 7810 IS-IS TE Metric Extensions May 20164.4. Unidirectional Link Loss Sub-TLV
This sub-TLV advertises the loss (as a packet percentage) between two
directly connected IS-IS neighbors. The link loss advertised by this
sub-TLV MUST be the packet loss from the local neighbor to the remote
one (i.e., the forward-path loss). The format of this sub-TLV is
shown in the following diagram:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A| RESERVED | Link Loss |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4
where:
Type: 36
Length: 4
A bit: The A bit represents the Anomalous (A) bit. The A bit is set
when the measured value of this parameter exceeds its configured
maximum threshold. The A bit is cleared when the measured value
falls below its configured reuse threshold. If the A bit is clear,
the sub-TLV represents steady-state link performance.
RESERVED: This field is reserved for future use. It MUST be set to 0
when sent and MUST be ignored when received.
Link Loss: This 24-bit field carries link packet loss as a percentage
of the total traffic sent over a configurable interval. The basic
unit is 0.000003%, where (2^24 - 2) is 50.331642%. This value is the
highest packet-loss percentage that can be expressed (the assumption
being that precision is more important on high-speed links than the
ability to advertise loss rates greater than this, and that high-
speed links with over 50% loss are unusable). Therefore, measured
values that are larger than the field maximum SHOULD be encoded as
the maximum value.
Previdi, et al. Standards Track [Page 9]

RFC 7810 IS-IS TE Metric Extensions May 20164.5. Unidirectional Residual Bandwidth Sub-TLV
This sub-TLV advertises the residual bandwidth between two directly
connected IS-IS neighbors. The residual bandwidth advertised by this
sub-TLV MUST be the residual bandwidth from the system originating
the Link State Advertisement (LSA) to its neighbor.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Residual Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 37
Length: 4
RESERVED: This field is reserved for future use. It MUST be set to 0
when sent and MUST be ignored when received.
Residual Bandwidth: This field carries the residual bandwidth on a
link, forwarding adjacency [RFC4206], or bundled link in IEEE
floating-point format with units of bytes per second. For a link or
forwarding adjacency, residual bandwidth is defined to be the Maximum
Bandwidth [RFC5305] minus the bandwidth currently allocated to RSVP-
TE label switched paths. For a bundled link, residual bandwidth is
defined to be the sum of the component link residual bandwidths.
The calculation of residual bandwidth is different than that of
unreserved bandwidth [RFC5305]. Residual bandwidth subtracts tunnel
reservations from maximum bandwidth (i.e., the link capacity)
[RFC5305] and provides an aggregated remainder across priorities.
Unreserved bandwidth, on the other hand, is subtracted from the
maximum reservable bandwidth (the bandwidth that can theoretically be
reserved) and provides per-priority remainders. Residual bandwidth
and unreserved bandwidth [RFC5305] can be used concurrently and each
has a separate use case (e.g., the former can be used for
applications like Weighted ECMP while the latter can be used for call
admission control).
Previdi, et al. Standards Track [Page 10]

RFC 7810 IS-IS TE Metric Extensions May 20164.6. Unidirectional Available Bandwidth Sub-TLV
This sub-TLV advertises the available bandwidth between two directly
connected IS-IS neighbors. The available bandwidth advertised by
this sub-TLV MUST be the available bandwidth from the system
originating this sub-TLV. The format of this sub-TLV is shown in the
following diagram:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Available Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5
where:
Type: 38
Length: 4
RESERVED: This field is reserved for future use. It MUST be set to 0
when sent and MUST be ignored when received.
Available Bandwidth: This field carries the available bandwidth on a
link, forwarding adjacency, or bundled link in IEEE floating-point
format with units of bytes per second. For a link or forwarding
adjacency, available bandwidth is defined to be residual bandwidth
(see Section 4.5) minus the measured bandwidth used for the actual
forwarding of non-RSVP-TE label switched path packets. For a bundled
link, available bandwidth is defined to be the sum of the component
link available bandwidths minus the measured bandwidth used for the
actual forwarding of non-RSVP-TE label switched path packets. For a
bundled link, available bandwidth is defined to be the sum of the
component link available bandwidths.
Previdi, et al. Standards Track [Page 11]

RFC 7810 IS-IS TE Metric Extensions May 20164.7. Unidirectional Utilized Bandwidth Sub-TLV
This sub-TLV advertises the bandwidth utilization between two
directly connected IS-IS neighbors. The bandwidth utilization
advertised by this sub-TLV MUST be the bandwidth from the system
originating this sub-TLV. The format of this sub-TLV is shown in the
following diagram:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Utilized Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6
where:
Type: 39
Length: 4
RESERVED: This field is reserved for future use. It MUST be set to 0
when sent and MUST be ignored when received.
Utilized Bandwidth: This field carries the bandwidth utilization on a
link, forwarding adjacency, or bundled link in IEEE floating-point
format with units of bytes per second. For a link or forwarding
adjacency, bandwidth utilization represents the actual utilization of
the link (i.e., as measured by the advertising node). For a bundled
link, bandwidth utilization is defined to be the sum of the component
link bandwidth utilizations.
5. Announcement Thresholds and Filters
The values advertised in all sub-TLVs (except min/max delay and
residual bandwidth) MUST represent an average over a period or be
obtained by a filter that is reasonably representative of an average.
For example, a rolling average is one such filter.
Min and max delay MUST each be derived in one of the following ways:
by taking the lowest and/or highest measured value over a measurement
interval or by making use of a filter or other technique to obtain a
reasonable representation of a min and max value representative of
the interval, with compensation for outliers.
Previdi, et al. Standards Track [Page 12]

RFC 7810 IS-IS TE Metric Extensions May 2016
The measurement interval, any filter coefficients, and any
advertisement intervals MUST be configurable per sub-TLV.
In addition to the measurement intervals governing re-advertisement,
implementations SHOULD provide configurable accelerated advertisement
thresholds per sub-TLV, such that:
1. If the measured parameter falls outside a configured upper bound
for all but the minimum delay metric (or lower bound for minimum
delay metric only) and the advertised sub-TLV is not already
outside that bound or,
2. If the difference between the last advertised value and current
measured value exceeds a configured threshold then,
3. The advertisement is made immediately.
4. For sub-TLVs that include an A bit, an additional threshold
SHOULD be included corresponding to the threshold for which the
performance is considered anomalous (and sub-TLVs with the A bit
are sent). The A bit is cleared when the sub-TLV's performance
has been below (or re-crosses) this threshold for an
advertisement interval(s) to permit fail back.
To prevent oscillations, only the high threshold or the low threshold
(but not both) may be used to trigger any given sub-TLV that supports
both.
Additionally, once outside the bounds of the threshold, any
re-advertisement of a measurement within the bounds would remain
governed solely by the measurement interval for that sub-TLV.
6. Announcement Suppression
When link-performance values change by small amounts that fall under
thresholds that would cause the announcement of a sub-TLV,
implementations SHOULD suppress sub-TLV re-advertisement and/or
lengthen the period within which they are refreshed.
Only the accelerated advertisement threshold mechanism described in
Section 5 may shorten the re-advertisement interval. All suppression
and re-advertisement interval backoff timer features SHOULD be
configurable.
Previdi, et al. Standards Track [Page 13]

RFC 7810 IS-IS TE Metric Extensions May 20167. Network Stability and Announcement Periodicity
Sections 5 and 6 provide configurable mechanisms to bound the number
of re-advertisements. Instability might occur in very large networks
if measurement intervals are set low enough to overwhelm the
processing of flooded information at some of the routers in the
topology. Therefore, care should be taken in setting these values.
Additionally, the default measurement interval for all sub-TLVs
SHOULD be 30 seconds.
Announcements MUST also be able to be throttled using configurable
inter-update throttle timers. The minimum announcement periodicity
is 1 announcement per second. The default value SHOULD be set to 120
seconds.
Implementations SHOULD NOT permit the inter-update timer to be lower
than the measurement interval.
Furthermore, it is RECOMMENDED that any underlying performance-
measurement mechanisms not include any significant buffer delay, any
significant buffer-induced delay variation, or any significant loss
due to buffer overflow or due to active queue management.
8. Enabling and Disabling Sub-TLVs
Implementations MUST make it possible to individually enable or
disable each sub-TLV based on configuration.
9. Static Metric Override
Implementations SHOULD permit static configuration and/or manual
override of dynamic measurements for each sub-TLV in order to
simplify migration and to mitigate scenarios where dynamic
measurements are not possible.
10. Compatibility
As per [RFC5305], unrecognized sub-TLVs should be silently ignored.
Previdi, et al. Standards Track [Page 14]

RFC 7810 IS-IS TE Metric Extensions May 201611. Security Considerations
The sub-TLVs introduced in this document allow an operator to
advertise state information of links (bandwidth, delay) that could be
sensitive and that an operator may not want to disclose.
Section 7 describes a mechanism to ensure network stability when the
new sub-TLVs defined in this document are advertised. Implementation
SHOULD follow the described guidelines to mitigate the instability
risk.
[RFC5304] describes an authentication method for IS-IS Link State
PDUs that allows cryptographic authentication of IS-IS Link State
PDUs.
It is anticipated that in most deployments, the IS-IS protocol is
used within an infrastructure entirely under control of the same
operator. However, it is worth considering that the effect of
sending IS-IS Traffic Engineering sub-TLVs over insecure links could
result in a man-in-the-middle attacker delaying real-time data to a
given site or destination, which could negatively affect the value of
the data for that site or destination. The use of Link State PDU
cryptographic authentication allows mitigation the risk of man-in-
the-middle attack.
12. IANA Considerations
IANA maintains the registry for the sub-TLVs. IANA has registered
the following sub-TLVs in the "Sub-TLVs for TLVs 22, 23, 141, 222,
and 223" registry:
Type Description
----------------------------------------------------
33 Unidirectional Link Delay
34 Min/Max Unidirectional Link Delay
35 Unidirectional Delay Variation
36 Unidirectional Link Loss
37 Unidirectional Residual Bandwidth
38 Unidirectional Available Bandwidth
39 Unidirectional Utilized Bandwidth
Previdi, et al. Standards Track [Page 15]